1. Field of the Invention
This invention relates to a process for producing a vinyl chloride polymer by suspension polymerization.
2. Description of the Prior Art
Vinyl chloride polymers are usually produced through the following steps: the steps of suspension polymerizing vinyl chloride or a monomer mixture containing vinyl chloride, in an aqueous medium in a polymerization vessel to obtain a polymer slurry; collecting unreacted monomers present in the polymerization vessel by evacuation and thereafter removing residual unreacted monomers from the polymer slurry by stripping; dehydrating the polymer slurry having passed through the stripping step, to obtain a polymer cake; and drying the polymer cake. This drying is usually carried out by the use of steam. Thus, the vinyl chloride polymer is obtained as a dried product.
In recent years, it is sought to shorten the time of polymerization production in order to improve productivity. As a part thereof, it is sought to shorten drying time in the drying step when the dried product of a vinyl chloride polymer is obtained. For this end, it is important to lower the water content of the polymer cake to be sent to the drying step after the dehydration. As methods of dehydration by which the water content in the polymer cake can effectively be lowered, a method is employed in which a centrifugal separator such as a screen bowl decanter type or solid bowl decanter type centrifugal separator is used as a dehydrator.
However, even when the dehydrator such as the centrifugal separator is used, the resulting polymer cake still has a water content ranging from 24 to 30% by weight. Such a water content is unsatisfactory from the viewpoint of making the drying time shorter, and it has been sought to make the polymer cake have a much lower water content.